1. Field of the Invention
This invention relates to multi-stage gearing apparatus and more particularly to an apparatus for distributing a source of energy to multiple rotational devices.
2. Description of the Prior Art
U.S. Pat. No. 6,304,002, granted on Oct. 16, 2001, describes a power train for an electric power-generating device in which wind or water currents turn a rotor. A torque-dividing gearbox is coupled to an input shaft driven by the rotor. The torque-dividing gearbox has a plurality of output shafts located around a perimeter of the input shaft. A number of torque-reducing gearboxes are each coupled to a respective one of the output shafts, each one of the torque-reducing gearboxes driving a generator. In one design the torque-reducing gearboxes and generators are held stationary and the torque-dividing gearbox includes a bull gear turned by the input shaft. Each one of the output shafts is connected to a gear that engages the bull gear teeth. Alternatively, the torque-reducing gearboxes and generators rotate with the input shaft. The torque-dividing gearbox includes a stationary ring gear having ring gear teeth around an inner circumference. Each of the output shafts is connected to a gear that engages the ring gear teeth.
U.S. Pat. No. 6,731,017 entitled “Improved Distributed power train That Increases Electric Power Generator Density” granted May 4, 2004 discloses an improvement of U.S. Pat. No. 6,304,002 in which a plurality of output shafts are located around a bull gear which is coupled to a main shaft. A number of generators are each coupled to a respective one of the output shafts, such that each one of the output shafts drives a generator. A number of intermediate gears are located around a perimeter of the bull gear, alternating half of the intermediate gears on one side of the bull gear and half on an opposite side of the bull gear. Each one of the intermediate gears is pressure fitted to an intermediate pinion with teeth that engage the bull gear teeth. Each one of the output shafts has two output pinions that engage adjacent intermediate gears, one intermediate gear on one side of the bull gear and one on an opposite side of the bull gear.
The tooth loads on the bull gear are divided n times, where n equals the number of generators, and tooth loads on the intermediate gears and high speed pinions are divided by n×2. This has the advantage that the lessened tooth loads allow for smaller gears and bearings, increasing power density and reducing mass and cost.
As turbines grow in size, the size and weight of individual components grow as well. Wind turbines place these components on top of a tower, presently stretching to over 100 meters above the ground, while ocean current turbines are located at sea, where they can only be accessed by boat. The size of the components necessitates very large lifting equipment, making both the land-based cranes and ocean lifting equipment extremely costly.
By dividing the power train into smaller components, generating systems receive an element of redundancy. For example, when ten small gearboxes and generators split the system's load, if one gearbox or generator experiences a fault, the system's capacity may only be reduced by 10%, allowing the system to remain active. A single generator system loses all of its capacity when the generator experiences a fault.
In wind and water turbine speed increasing systems and other power generation and motoring systems, a high gear ratio is needed, particularly as the size of rotor blades grows and their speed declines. A high gear ratio causes a generator to run at higher speed, lowering its size and cost. A typical prior wind or water turbine power train has three or four step-up stages to achieve the desired gear ratio.
It is therefore desirable to provide a gear configuration that provides large step-up gear ratios in just two steps.
In the prior art, generator rotors are usually supported on a bearing system that is contained within the outside casing of the generator. Bearings are usually lubricated with grease to avoid the expense of a circulating oil system. For very extended life, oil needs to be filtered to remove contamination introduced by wear particles and by environmental intrusion. Grease must be replenished. This results in undesirable maintenance and disposal of hazardous materials.
It is desirable to provide a gearbox-generator combination in which the generator bearings are eliminated.
Gear noise is very objectionable in wind turbines, leading to use of isolators to mount transmissions to wind turbine frames. These isolators contain rubber elements and have a finite fatigue life. They are in the load path of a highly loaded system and are therefore difficult to replace.
It is desirable to provide a gearbox-generator combination in which the generator noise is optimized and isolator gearbox mounts and their attendant cost and maintenance are eliminated.